This proposal outlines a basic research plan for studying the mechanism by which calcium binding proteins regulate excitation-coupled events such as contraction and secretion. In particular, the action and interaction of calcium ions and cyclic nucleotides as key elements in the control of neurotransmitter release from nervous issue will be investigated. The role of a low molecular weight-high affinity calcium binding protein found in the adrenal medulla (AM-CBP) in modulating cyclic nucleotide levels and in regulating the calcium-sensitive actomyosin interaction is being investigated. The study of the fundamental role of AM-CBP in the celcium dependent regulation of a neurosecretory system such as the adrenal medulla will provide a block of information which may apply not only to nerve tissue but also to regulatory events in other secretory tissues.